A family of structurally related intrinsic membrane proteins (facilita
tive glucose transporters) catalyzes the movement of glucose across th
e plasma membrane of animal cells. Evidence indicates that these prote
ins show a common structural motif where approximately 50% of the mass
is embedded in lipid bilayer (transmembrane domain) in 12 alpha-helic
es (transmembrane helices; TMHs) and accommodates a water-filled chann
el for substrate passage (glucose channel) whose tertiary structure is
currently unknown. Using recent advances in protein structure predict
ion algorithms we proposed here two three-dimensional structural model
s for the transmembrane glucose channel of GLUT1 glucose transporter.
Our models emphasize the physical dimension and water accessibility of
the channel, loop lengths between TMHs, the macrodipole orientation i
n four-helix bundle motif, and helix packing energy. Our models predic
t that five TMHs, either TMHs 3, 4, 7, 8, 11 (Model 1) or TMHs 2, 5, 1
1, 8, 7 (Model 2), line the channel, and the remaining TMHs surround t
hese channel-lining TMHs. We discuss how our models are compatible wit
h the experimental data obtained with this protein, and how they can b
e used in designing new biochemical and molecular biological experimen
ts in elucidation of the structural basis of this important protein fu
nction.